Mix & Match & Tekmar 256

JasonA

I am trying to work out the schematic wiring of installing a Tekmar 256 into my system that has both a circulator serving 4 zone valved zones and two additional zones served by their own individual circulators. The circulator serving the zone valves is controlled by the integral to the boiler Honeywell L8148E connected to terminals C1 and C2. The thermostats for each of the zones are wired through the end switches in the zone valves and connected to terminals TV and T on the L8148E. The other two individually circulator zones are wired through TACO SR501 Pump Relays. Terminals 5 and N/O 6 are connected to terminals Z and B on the L8148E. A call for heat on these zones retains the high limit controller on the L8148E but does not energize the relay and engage the circulator serving the zone vale zones.



Enter the Tekmar 256. The only way I have seen to connect the 256 (without buying another pump relay for the zone valved zones) is inserting it in series with the ignition control (Honeywell S8610U), using terminals 5 and 6. Terminals 7 and 9 would be jumped out. Other than losing the display information on the 256 (Boiler demand will always be indicated) is there any other problem with my proposed installation or better yet how can I better wire the 256 into my current configuration?



Thanks for your help.



Attached is the wiring diagrams for the various components of this system.

Steamhead

Are the zone valves

3-wire or 4-wire units?

JasonA

4- wire - wired as three

Honeywell V8043E1012 - Standard normally closed 24V with an end switch. Wired as shown on Figure 8 of the L8148E diagram

JStar

RE

I would not jump out the Tekmar Demand terminals or it will always want to fire the boiler. You should wire the Tekmar boiler contacts in series with the wire going to TH-W on the spark module. That will let the Tekmar act as the high limit. Set the aquastat for 20F higher than the Tekmar limit.



To create a "call for heat", you could do a few things. The easiest would be to run B1 and B2 to 7 and 9 on the Tekmar. Then jumper 7 and 8. The Tekmar would only be powered with a call for heat, so you'd have a blank screen when there is no call. Could be annoying. This sounds okay in theory, but I would predict a lot of quirky issues associated with this set-up.



The other way is to add another relay into the circuit. Have the L8148E energize the coil from the B1/B2 circuit. One set of contacts will send power to the spark module. The other contacts send the Tekmar's signal back to itself as a call for heat through 7 and 9.



And remember...use fuses!

Steamhead

With a three-wire ZV

you're outputting 24V to something, rather than closing a switch. What I'd do is power the ZVs with a fan-center relay setup having DPDT switching (and its own transformer of course). Honeywell's model number for this is R8239A1052. Wire the switched outputs from all the ZVs to the relay terminal (I think it's G but not completely sure) on the fan center. This way when any zone valve opens it will operate the relay.



The R8239A's DPDT switching allows you to control two separate items. Use one set of contacts to operate the circulator, and the other to close the "boiler demand" terminals on the 256. The 256 would then close TT on the L8148E, starting the burner (but not the circulator, the R8239 controls that now).



I've used this setup with Taco 570-series ZVs and it works well.